Clearcoat-basecoat composite coatings are widely used in the coatings art and are notable for desirable gloss, depth of color, distinctness of image and/or special metallic effects. Composite systems are particularly utilized by the automotive industry to achieve advantageous visual effects, especially a high degree of clarity. However, a high degree of clarity in the clearcoat makes it easier to observe defects. Defects resulting from environmental etch are particularly disadvantageous. Environmental etch is a phenomenon which manifests as spots or marks on or in the clearcoat which are removed only with loss of clearcoat.
Clearcoat compositions containing carbamate-functional acrylic polymers have been disclosed by the prior art as a solution to the problem of environmental etch.
While such polymers and compositions containing them provide a significant improvement over the prior art, improvements in some areas are still desirable. In particular, it would be advantageous to provide polymers exhibiting improved adhesion while still possessing the positive environmental etch and performance characteristics of carbamate-functional acrylics. Improvements are particularly desired with respect to adhesion of the polymer-containing composition to one or more subsequently applied coatings or materials.
For example, surfaces coated with clearcoat-basecoat compositions must sometimes be repaired or treated to correct minor defects or flaws. Such repairs often require the application of subsequently applied basecoat/clearcoat composite compositions, basecoat or clearcoat compositions alone, or fast cure versions thereof. That portion of the originally applied clearcoat composition must adhere to the subsequently applied basecoat/clearcoat composite composition, basecoat or clearcoat compositions alone, and/or any other subsequently applied material or materials. Adhesion failures resulting from a weak bond between the originally applied coating and the subsequently applied coating or material are known as intercoat adhesion failures. Intercoat adhesion is thus a required characteristic of coating compositions intended for use in clearcoat-basecoat compositions, especially for clearcoat compositions intended for use in the automotive OEM markets.
While carbamate-functional polymers and compositions incorporating the same have been disclosed in the prior art to have advantageous properties, intercoat and repair adhesion issues remain unaddressed.
For example, U.S. Pat. No. 5,412,049 discloses copolymers which are the copolymerization product of (a) hydroxyl (meth)acrylate ester monomers and (b) (meth)acrylate esters of hydroxyalkyl carbamate monomers. Other comonomers based on (meth)acrylate homopolymers or copolymers and optional ethylenically unsaturated monomers may be copolymerized with the fumctional components (a) and (b) in amounts of from about 0 to 90 weight percent of the total copolymer composition, more preferably from 10 to 80 weight percent of the total copolymer composition, most preferably from about 20 to 70 weight percent of the total copolymer composition.
However, adhesion, especially intercoat adhesion, is not discussed in the '049 patent. Moreover, all of the working examples require the use of 55 weight percent or more of nonfunctional ethylenically unsaturated monomers.
U.S. Pat. No. 5,356,669 provides a curable coating composition comprising (a) a first component comprising a polymer backbone having appended thereto at least one carbamate-functional group, and (b) a second component comprising a compound having a plurality of functional groups that are reactive with said carbamate group. The polymer component (a) is represented by the formula: In this formula, A represents repeat units derived from one or more ethylenically unsaturated monomers such as alkyl esters of acrylic or methacrylic acid, e.g., ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate, isodecyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and the like; and vinyl monomers such as unsaturated m-tetramethyl vinyl isocyanate, styrene, vinyl toluene and the like. x and y represent weight percentages, with x being 10 to 90% and preferably 40 to 60%, and y being 90 to 10% and preferably 60 to 40%.
Thus, the prior art has failed to achieve a carbamate functional polymer having the desired adhesion to subsequently applied materials.
Accordingly, it is an object of the invention to provide carbamate-flnctional polymers that exhibit improved adhesion to subsequently applied materials while maintaining the known advantages of carbamate-functional polymers.
It is a further object of the invention to provide coating compositions containing such carbamate-functional polymers.
It is another object of the invention to provide a method of making a carbamate-functional polymer having improved intercoat adhesion properties as well as carbamate-functional polymers made from such a method.
These and other objects of the invention have been achieved by the instant invention.
It has unexpectedly been found that use of less than 35 percent by weight of nonfunctional monomers based on the total weight of the polymer, preferably less than 20 percent and most preferably less than 10 percent, results in desirable improvements in adhesion, especially recoat adhesion. Even more unexpectedly, it has been found that such improvements in adhesion can be obtained without the loss of any of the desirable performance, reactivity and/or application characteristics associated with carbamate-functional acrylics.